In process for producing semiconductors, the photolithography technology has been widely used in patterning circuits on substrates. In the photolithography technology, it requires using of photosensitive resins. Due to the photo-sensitivity of the resins, a printed circuit board having a desired pattern could be obtained by exposing the photosensitive resin to radiation through a patterned mask, developing, and removing the exposed part or the unexposed part with an aqueous alkaline solution.
Many kinds of photosensitive resins have been developed and used in the photolithography technology. For example, U.S. Pat. No. 5,587,275 disclosed a polyimide precursor which has a structure unit shown in the following formula (1):
wherein X is a tetra-valence organic group having an aromatic ring; Y is a two-valence organic group having an aromatic ring; Z is a hydrogen atom or acryloyloxy or methacryloyloxy as shown in the following formula (2):
wherein R is a hydrogen atom or a methyl group.
In U.S. Pat. No. 5,587,275, a diamine is firstly reacted with (meth)acryl glycidyl ether to produce diamine monomer having acryloyloxy group, then the resultant diamine monomer is reacted with a tetra-carboxylic acid dianhydride to procure a polyimide precursor of the above formula (1).
Furthermore, in U.S. Pat. No. 6,025,113, it disclosed a polyimide precursor having repeat units of the following formula (3) and (4):
wherein R1 is a tetra-valence organic group having 4 or more carbon atoms; R2 is a three- or four-valence organic group having at least one aryl group; R3 is a mono-valence organic group; A is an acidic mono-valence group; and n is 1 or 2;
wherein R1 is a tetra-valence organic group having 4 or more carbon atoms; R3 is a mono-valence organic group; R4 is a two-valence organic group having at least one aromatic ring or silicon atom.
In U.S. Pat. No. 6,025,113, the photo-resist sensitivity of polyimide precursor is increased through the formation of ester group between acryloyl and polyamic acid. The polyimide precursor is exposed and developed, finally cyclized at an elevated temperature to form a polyimide having superior heat-resistance and flexibility.